Understanding Human Evolution: The Special Function of Our Foot Arch as a Spring

New research posits that the distinctive arch of the human foot evolved to enhance bipedal walking and running, behaving as a spring and rebounding to set the ankle upright for effective thrust. This finding deviates from prior theories suggesting the arch functioned as a lever and could offer insights into the evolution of bipedalism and possibly refine treatments for individuals with foot ailments.

Scientists have unearthed that our foot’s flexible arch could have been pivotal in our ability to run and walk upright.

Recent research indicates that the human’s unique spring-like foot arch evolution might have been essential for bipedal walking. Long-standing theories among researchers studying bipedalism proposed that the foot’s elevated arch functioned as a lever, facilitating forward propulsion during walking.

However, an international group of scientists has found that the spring-like motion of the flexible arch assists in realigning the ankle upright, thereby boosting walking efficiency. The advantages are more noticeable during running, suggesting the requirement for effective running may have spurred the evolution of a flexible arch, improving walking efficiency as well. This newfound comprehension could lead to improved treatments for contemporary patients with foot ailments.

“We initially assumed that the spring-like arch aided in propelling the body into the subsequent step,” said Dr. Lauren Welte, the study’s lead author, published in Frontiers in Bioengineering and Biotechnology. “However, we discovered that the spring-like arch rebounds to assist the ankle in lifting the body.”

Evolution step by step

The evolution of our feet, notably the raised medial arch which differentiates us from great apes, is vital to bipedal walking. When arch motion is limited, running requires more energy, suggesting the arch provides leverage for upright walking. Arch recoil could potentially increase our running efficiency by driving the body’s center mass forward or compensating for the mechanical work muscles would otherwise perform.

To explore these suppositions, the research team chose seven participants with varying arch flexibility, who walked and ran while high-speed x-ray motion capture cameras filmed their feet.

Each participant’s arch height was measured, and their right feet were CT-scanned. The scientists fabricated rigid models and contrasted them with the measured foot bone motions to examine the impact of arch flexibility on adjacent joints. They also analyzed which joints contributed most to arch recoil and its influence on the center of mass and ankle propulsion.

Towards bipedalism

While scientists anticipated that arch recoil would aid the arch’s rigid lever in lifting the body, they discovered that a rigid arch without recoil led to an early foot lift-off, probably reducing calf muscle efficiency, or caused the ankle bones to lean too far forward. This forward leaning reflects the walking posture of chimpanzees rather than the upright stance typical of human gait.

The flexible arch helped realign the ankle upright, allowing the leg to push off the ground more effectively. This influence is even greater when running, suggesting that efficient running may have provided evolutionary pressure favoring the flexible arch.

Researchers also found that the joint between the navicular and medial cuneiform bones in the medial arch is crucial for arch flexibility. Modifications to this joint could assist in tracing the bipedalism evolution in the hominin fossil record.

“The flexibility of our feet seems to enable us to walk and run upright rather than either leaning forward or taking the next step too prematurely,” said Dr. Michael Rainbow of Queen’s University, the senior author.

Therapeutic possibilities

These discoveries also imply therapeutic possibilities for individuals with rigid arches due to injury or disease: enhancing the arch’s flexibility could improve overall mobility.

“Our research suggests that enabling arch movement during propulsion makes movement more efficient,” Welte said. “If we limit arch motion, it’s likely that there are corresponding changes in how the other joints function.”

Rainbow added, “At this point, our hypothesis requires further validation because we need to confirm whether variations in foot flexibility across the population lead to the kinds of changes observed in our limited sample. However, our work paves the way for an exciting new line of investigation.”

The study, titled “Mobility of the human foot’s medial arch helps enable upright bipedal locomotion” by Lauren Welte, Nicholas B. Holowka, Luke A. Kelly, Anton Arndt, and Michael J. Rainbow, was published on 30 May 2023 in Frontiers in Bioengineering and Biotechnology.

The research received funding from the Government of Ontario, the Natural Sciences and Engineering Research Council of Canada, and the Pedorthic Research Foundation of Canada.

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More about Human foot arch evolution

• Exploring the Evolution of Human Bipedalism
• The Biomechanics of Running
• Human Foot and Ankle Biomechanics
• Insights into Hominin Evolution from the Fossil Foot Record
• Understanding the Function of Human Foot Arches